Amsterdam - The Dutch royal family was to have additional security in place at a World War II memorial ceremony Monday following an attack on their open-top bus that left seven bystanders dead last week.

The measures would result in a ceremony taking place in the city of Amsterdam at 8 pm (1800 GMT) with less space for public participation.

Increased security around the Dutch royals comes in the wake of an attack in which a 38-year-old man drove his car into a crowd watching the Queen's Day procession.

He had reportedly intended to hit the royal bus but instead killed seven and injured 12 people in the crowd attending the event in the town of Apeldoorn, 90 kilometres east of Amsterdam.

"We would like to maintain an open character of the WWII memorial. However, extra security measures have resulted in less room for the public during the memorial," a spokesman for Amsterdam Mayor Job Cohen.

The participation of Queen Beatrix, Crown Prince Willem-Alexander and his wife Princess Maxima would mark their first public appearance since the attack.

The city of Amsterdam confirmed it has also stepped up its security measures for Liberation Day events on Tuesday, while some programmes have been adjusted and given a more solemn character.

Queen Beatrix is due to attend a Liberation Day open-air concert near the Amstel river.

Beatrix's youngest son, Prince Constantijn, has said that despite the attack, he supports the continued "open and informal character" of Queen's Day.

Dutch royals traditionally mingle with the audience and participate in the celebrations on that day.

Authorities in Belgium have meanwhile taken precautionary measures to protect Belgian royals who are due to attend a parade scheduled for July 20, according to television reports in the Netherlands.

The reports said Belgian authorities feared the Dutch incident might give people the idea the Belgian royals would be an "easy target." (dpa)